Method of preventing toppling of lower electrode through flush cleaning

ABSTRACT

A method of forming the lower electrode of a capacitor capable of withstanding the flushing force produced by a cleaning agent. A lower electrode having a rectangular profile when viewed from the top is provided. The lower electrode is bounded by a pair of ends and a pair of sides. The ends and the sides are linked together. The ends have a wedge shape. The sides have edges that cave in towards the center, thereby forming a recess region between the sides. A flushing operation is carried out using a cleaning solution. The cleaning solution flows from one end of the electrode to the other end along the sides.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The present invention relates to a semiconductor structure. Moreparticularly, the present invention relates to the lower electrodestructure of a capacitor that can withstand the flushing force producedby a cleaning agent.

[0003] 2. Description of Related Art

[0004] Capacitor is the data storage section of a dynamic random accessmemory (DRAM). Data value of each memory cell is recorded as the amountof charges carried by the capacitor. Due to the miniaturization ofmemory cells, each cell is very small. To increase the capacitance of acapacitor and to reduce data errors and the number of memory refreshes,height of the lower electrode is frequently raised to increase theeffective surface area of a capacitor.

[0005]FIG. 1 is a schematic cross-sectional view of the lower electrodeof a conventional capacitor. To fabricate a conventional capacitor, aplurality of metal-oxide-semiconductor MOS transistors is formed over asubstrate 100. Each MOS transistor includes a gate electrode 102 abovethe substrate 100, spacers 104 on the sidewalls of the gate electrode102 and source/drain regions 106 in the substrate 100 on each side ofthe gate electrode 102. A dielectric layer 108 is formed over thesubstrate 100 covering the MOS transistor. A bit line 110 is formed inthe dielectric layer 108. The bit line 110 is electrically connected toone of the source/drain terminals 106. Another dielectric layer 112 isformed over the substrate 100 covering the bit line 110. A plurality oflower electrodes 114 that pass through the dielectric layers 108 and 112is formed with each lower electrode 114 electrically connected to asource/drain terminal 106.

[0006]FIG. 2 is a top view showing a plurality of conventional capacitorlower electrodes on a substrate. As shown in FIG. 2, a conventionallower electrode 114 has a rectangular shape. Before carrying out otherprocessing treatment such as the growth of hemispherical silicon grainsover the electrode for increasing effective surface area or thedeposition of a capacitor dielectric layer, RCA cleaning solution isused to clean the surface. The RCA solution contains de-ionized water,sulfuric acid (H₂SO₄) and hydrogen peroxide (H₂O₂). The cleaning processincludes repeated flushing of the lower electrodes 114 with de-ionizedwater, sulfuric acid solution and hydrogen peroxide solution.

[0007] However, as size of each memory cell is reduced, height of thecapacitor lower electrode 114 must increase correspondingly tocompensate for the shrinkage in surface area so that sufficient chargestorage capacity is still present. Yet, the increase in height makes thelower electrode 114 more vulnerable to tearing when RCA solution is usedto clean the surface. FIG. 3 is a top view showing the array ofcapacitor lower electrodes after flushing with a cleaning solution. Asshown in FIG. 3, a few of the lower electrodes 114 are flushed away fromtheir original positions into new positions 114 a. Due to the flushingdamages, production yield of the process is lowered.

SUMMARY OF THE INVENTION

[0008] Accordingly, one object of the present invention is to provide amethod of forming the lower electrode of a capacitor capable ofwithstanding the flushing force produced by a cleaning agent. A lowerelectrode having a rectangular profile when viewed from the top isprovided. The lower electrode is bounded by a pair of ends and a pair ofsides. The ends and the sides are linked together. The ends have a wedgeshape. The sides have edges that cave in towards the center, therebyforming a recess region between the sides. A flushing operation iscarried out using a cleaning solution. The cleaning solution flows fromone end of the electrode to the other end along the sides.

[0009] This invention also provides an alternative method of forming thelower electrode of a capacitor capable of withstanding the flushingforce produced by a cleaning agent. The lower electrode is a rectangularprism and has an hourglass shape when viewed from the top. The two sidesof the lower electrode are edges that cave in towards the center. Arecess region is defined between the two sides. A flushing operation iscarried out using a cleaning solution. The cleaning solution flows fromone end of the lower electrode to the other along the two sides of thelower electrode.

[0010] The step of flushing the lower electrodes can be carried outbefore other processing treatment such as the growth of hemisphericalsilicon grains over the electrode for increasing effective surface areaor the deposition of a capacitor dielectric layer. The cleaning processincludes repeated flushing of the lower electrodes with solutions suchas de-ionized water, sulfuric acid solution and hydrogen peroxidesolution.

[0011] The capacitor lower electrode structure of this invention has anhourglass profile and hence a more streamline body. According to fluiddynamics, resistant towards fluid motion is smaller. Consequently, thecleaning solution rushing past the lower electrode will cause lessshearing and hence will result in the least damage. Furthermore, surfacearea of the lower electrode is also more than a conventional lowerelectrode, thereby increasing capacitance of the capacitor.

[0012] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary, andare intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

[0014]FIG. 1 is a schematic cross-sectional view of the lower electrodeof a conventional capacitor;

[0015]FIG. 2 is a top view showing a plurality of conventional capacitorlower electrodes on a substrate;

[0016]FIG. 3 is a top view showing the array of capacitor lowerelectrodes after flushing with a cleaning solution;

[0017]FIG. 4 is a top view showing an array of capacitor lowerelectrodes according to one preferred embodiment of this invention;

[0018]FIG. 5 is a top view showing a capacitor lower electrode accordingto one preferred embodiment of this invention; and

[0019]FIG. 6 is a diagram from the top outlining fluid motion paths whena cleaning solution is used to flush the capacitor lower electrodes ofthis invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

[0021]FIG. 4 is a top view showing an array of capacitor lowerelectrodes according to one preferred embodiment of this invention. Asshown in FIG. 4, this invention provides a special type of lowerelectrode structure 116 for a capacitor. The capacitor lower electrode116 is a rectangular prism having a side profile similar to the oneshown in FIG. 1. Since the positioning of the array of lower electrodesis similar to a conventional arrangement, detailed description is notrepeated here. FIG. 5 is a top view showing a capacitor lower electrodeaccording to one preferred embodiment of this invention. Aside from adifference in shape for the lower electrode, other aspects are the same.Hence, the labels in FIGS. 1 to 3 are reused.

[0022] As shown in FIG. 5, the electrode has a rectangular outline 124very similar to an hourglass viewed from the top. The lower electrode124 is bounded by a pair of sides 118 and a pair of ends 120. The sides118 and the ends 120 are linked together. The sides 118 are edges thatcave in towards the center, thereby forming an hourglass profile. Arecess region 122 is defined between the sides 118. The ends of thelower electrode 124 can have a wedge shape. The lower electrode 116 canbe made using polysilicon, for example.

[0023]FIG. 6 is a diagram from the top outlining fluid motion paths whena cleaning solution is used to flush the capacitor lower electrodes ofthis invention. Before carrying out other processing treatment such asthe growth of hemispherical silicon grains over the electrodes 116 forincreasing effective surface area or the deposition of a capacitordielectric layer, the surface having the electrodes thereon must becleaned. As shown in FIG. 6, the substrate 100 is positioned at adefinite angle with respect to the horizontal. The surface of withelectrodes 116 is flushed using a cleaning solution 126. The cleaningsolution 126 flows from one end 120 of the electrode 116 to the otherend 120 along the sides 118. For example, a RCA cleaning solution may beused to clean the electrode surface. The RCA solution containsde-ionized water, sulfuric acid and hydrogen peroxide. Alternatively,the lower electrodes 116 are repeated flushed by deionized water,sulfuric acid solution and hydrogen peroxide solution.

[0024] The capacitor lower electrode structure 116 of this invention hasa more streamline body. According to fluid dynamics, resistant towardsfluid motion is smaller. Consequently, the RCA cleaning solution rushingpast the lower electrode will cause less shearing and hence will resultin the less damage. Furthermore, surface area of the lower electrode isalso more than a conventional lower electrode, thereby increasingcapacitance of the capacitor.

[0025] It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A method of shaping the lower electrode of acapacitor for minimizing shearing damage during surface flushing,comprising the steps of: providing a lower electrode in the form of arectangular prism and a rectangular shape viewed from the top, whereinthe rectangular shape is bounded by a pair of ends and a pair of sides,the ends and sides are linked together and the sides has edges that cavein towards the center, and a recess region is defined between therespective sides; and flushing the lower electrode with a cleaningsolution in such a way that the cleaning solution moves from one end ofthe electrode to the other end along the sides.
 2. The method of claim1, wherein material constituting the lower electrode includespolysilicon.
 3. The method of claim 1, wherein the ends have a wedgeshape.
 4. The method of claim 1, wherein the step of flushing the lowerelectrode includes cleaning the surface of the lower electrode.
 5. Themethod of claim 4, wherein the step of cleaning the surface of the lowerelectrode includes flushing the lower electrode repeatedly withde-ionized water, sulfuric acid solution and hydrogen peroxide.
 6. Amethod of shaping the lower electrode of a capacitor for minimizingshearing damage during surface flushing, comprising the steps of:providing a lower electrode having an hourglass profile when viewed fromthe top, wherein the lower electrode has a pair of sides with edges thatcave in towards the center, and a recess region is defined between therespective sides; and flushing the lower electrode with a cleaningsolution in such a way that the cleaning solution runs along the sidesof the electrode.
 7. The method of claim 6, wherein materialconstituting the lower electrode includes polysilicon.
 8. The method ofclaim 6, wherein the step of flushing the lower electrode includescleaning the surface of the lower electrode.
 9. The method of claim 8,wherein the step of cleaning the surface of the lower electrode includesflushing the lower electrode repeatedly with de-ionized water, sulfuricacid solution and hydrogen peroxide.